1. Field of the Invention
The present invention relates to a magnetic recording method in which data is recorded by changing a magnetization state of a magnetic recording medium, and more particularly, to a magnetic recording method for recording ternary data using a characteristic of a read head, a pre-amplifier circuit, and a magnetic recording apparatus utilizing same.
This application claims the benefit of Korean Patent Application No. 10-2006-0010581, filed on Feb. 3, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
2. Discussion of Related Art
Hard disk drives (HDDs) are recording devices used to store binary information on concentric tracks of a magnetic disk. The disk is rotatably mounted on a spindle motor, and information is accessed by a head attached to an actuator or flexure arm rotated by a voice coil motor (VCM). The VCM rotates the actuator by a VCM driving current, thereby moving the head across the surface of the disk.
The head reads information recorded on the surface of the disk by sensing a magnetic field on the surface or writes information on the disk by magnetizing the surface of the disk. A write current is supplied to the head to write the data, thereby generating a magnetic field from the head. In an HDD using a longitudinal recording method, a magnetic disk is magnetized in one of two opposite directions along the centerline of each track. In a perpendicular recording method, a magnetic disk is magnetized in one of up and down directions along a perpendicular line to the surface of the disk.
FIG. 1 is a plan view of a conventional HDD 100 that includes at least one disk 12 rotated by a spindle motor 14 and at least one head 16 located above the surface of the disk 12. Head 16 can read or write information from or to disk 12 by sensing a magnetic field on the surface of the disk 12 or by magnetizing the surface of the disk 12. Head 16 includes a write head for magnetizing disk 12 and a separate read head for sensing a magnetic field on disk 12. The head 16 is mounted on a slider (not shown) combined with suspension arm 20. The slider generates air between head 16 and the surface of disk 12 to maintain head 16 a distance above the disk. Suspension 20 is combined with a head stack assembly (HSA) 22 which is attached to an actuator arm 24 having a voice coil 26. Voice coil 26 is located adjacent to magnetic assembly 28 supporting VCM 30 that supplies a driving current supplied to the voice coil 26 to generate a torque to rotate actuator arm 24 around a bearing assembly 32. The rotation of the actuator arm 24 moves head 16 across the surface of disk 12.
FIG. 2 is a schematic diagram illustrating a conventional perpendicular recording method. Head 16 includes a write head 33 recording a signal in a recording layer 36 using a magnetic induction method and a read head 34 reading an electrical signal from the recording layer 36 of disk 12. Write head 33 records a signal by applying a magnetic field in the perpendicular direction corresponding to binary values (i.e. 0 and 1) of data to be recorded to recording layer 36. The magnetization states of recording layer 36 are illustrated using up arrows and down arrows. For example, recording layer 36 may have a magnetization state (a first magnetization state) indicated by an up arrow and a magnetization state (a second magnetization state) indicated by a down arrow. Read head 34 generates an electrical signal by detecting the magnetic flux density and direction of the recorded signal on layer 36. Read head 34 may be, for example, giant magnetic resistive (GMR) head and a tunneling magnetic resistive (TuMR) head.
FIG. 3 is a graph showing a correlation between the detection width PW50 of the read head 34 and the minimum write width PWmin and shows a read signal corresponding to the minimum write width PWmin. The detection width PW50 of read head 34 is designed to be narrower than the minimum write width PWmin of a recorded signal on recording layer 36 of disk 12 (i.e., the minimum length with which the signal is recorded on the surface of the disk), because the intensity and direction of magnetic flux cannot be detected by read head 34 if the detection width PW50 of read head 34 is wider than the minimum write width PWmin. In particular, detection width PW50 of read head 34 is indicated by a pulse width having a magnitude corresponding to 50% of the peak intensity of a read signal corresponding to the minimum write width PWmin. The detection width PW50 is defined as a distance PW50 (pulse width at 50% of peak intensity) between a position corresponding to 50% of the peak intensity in the rising edge and a position corresponding to 50% of the peak intensity in the falling edge of the read signal. Thus, a correlation of PW50<PWmin is satisfied and the recording density of an HDD is determined by the detection width PW50 of read head 34.
FIGS. 4A through 4G are signal diagrams to illustrate a write/read process in a conventional HDD using the longitudinal recording method where, FIG. 4B shows a write current, FIG. 4C shows a magnetization transition state of the recording layer 36, FIG. 4D shows a read signal detected by the read head 34, FIG. 4E shows a differentiated signal obtained by performing differential of first order for the read signal of FIG. 4D, FIG. 4F shows a clock signal, and FIG. 4G shows a data output.
FIG. 4A shows a data clock where period T is determined by the minimum write width PWmin and the detection width PW50 of read head 34. The write current illustrated in FIG. 4B generates a magnetic field corresponding to data to be recorded on the disk surface. A current in a forward direction (first direction), which has a predetermined magnitude, is applied to write head 33 during a period indicated by “1,” and a current in a reverse direction (second direction) opposite to the first direction is applied to write head 33 during a period indicated by “0.” Thus, opposite magnetic fields are generated from write head 33 by currents in the forward and reverse directions.
The recording layer 36 of the disk 12 is magnetized by the magnetic fields generated by write head 33 as illustrated in FIG. 4C. For example, recording layer 36 is consecutively magnetized in the forward direction during a period in which data has a value of “1” and in the reverse direction during a period in which data has a value of “0.” The length of the period in which data has a “1” or “0” is at least greater than the minimum write width PWmin (commonly, in 1 T to 11 T, T denotes the period of the data clock. The magnetization state of recording layer 36 is detected by read head 34. The read signal is reversed at a position (a transition position) at which the magnetization state of recording layer 36 is reversed. Thus, the transition position can be detected from a zero crossing point of the differentiated signal illustrated in FIG. 4E obtained by differentiating the read signal illustrated in FIG. 4D. That is, the data output illustrated in FIG. 4G can be obtained by waveform shaping the differentiated signal illustrated in FIG. 4E and sampling the waveform-shaped differentiated signal by synchronizing it with the clock signal illustrated in FIG. 4F which has the same period T of the data clock.
In conventional recording methods describing above, the recording layer 36 of the disk 12 is consecutively magnetized in the right (forward) or left (reverse) direction during at least the minimum write width PWmin. That is, for the recording layer 36, areas corresponding to the minimum write width PWmin can have only a magnetization state of the forward or reverse direction. Thus, a drawback in conventional recording methods is that an increase in recording density can only be achieved by a decrease in the minimum write width PWmin (i.e., improvement of the detection width of read head 34 or improvement of the quality of disk 12). Thus, data cannot be recorded with recording density higher than that determined by the detection width of the read head 34.